kuliah iii- protein 2010
TRANSCRIPT
Kuliah III. ProteinStruktur dan Fungsi
SEL: Arsitektur dan Senyawa dalam Sel
Air Karbohidrat Lipid Vitamin & Mineral Protein Asam Amino Asam Nukleat
Shape = Amino Acid Sequence
Proteins are made of 20 amino acids linked by peptide bonds
Polypeptide backbone is the repeating sequence of the N-C-C-N-C-C… in the peptide bond
The side chain or R group is not part of the backbone or the peptide bond
Polypeptide backbone
Amino AcidsNOTE: You need to know this table
HYDROPHILIC HYDROPHOBIC
Struktur Asam Amino
Protein-clasified by function
Make up about 15% of the cell, have many function in the cell:
1. ENZYME : catalytic activity and function2. TRANSPORT : bind & carry ligands3. STORAGE : ovalbumin, casein4. CONTRACTILE (MOTOR): can contract, change shape 5. STRUCTURAL : keratin of hair, feathers, & nails, fibroin
of silk & webs6. DEFENSIVE (PROTECT): antibody, snake venom7. REGULATORY (SIGNAL): hormones8. RECEPTORS (DETECT STIMULI): light & rhodopsin
Protein structure
Primary structure: amino acid sequence
Secondary structure: folding of single polypeptide chains
Tertiary structure: 3-dimensional shape of proteins
Quaternary structure: joining of polypeptide chains into proteins
.
Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.
linear sequence of peptides
each peptide is several amino acids
frequently highly folded
.
Struktur Primer:
Urutan asam-asam amino yang membentuknya, terikat satu sama lain dengan ikatan peptida.
The primary structure of a protein is its unique sequence of amino acids.
Lysozyme, an enzyme that attacks bacteria, consists on a polypeptide chain of 129 amino acids.
The precise primary structure of a protein is determined by inherited genetic information.
Protein Folding
The peptide bond allows for rotation around it and therefore the protein can fold and orient the R groups in favorable positions
Weak non-covalent interactions will hold the protein in its functional shape – these are weak and will take many to hold the shape
Non-covalent Bonds in Proteins
Hydrogen Bonds in Proteins
H-bonds form between 1) atoms involved in the peptide bond; 2) peptide bond atoms and R groups; 3) R groups
Protein Folding (continued)
Proteins shape is determined by the sequence of the amino acids
The final shape is called the conformation and has the lowest free energy possible
Denaturation is the process of unfolding the protein Can be down with heat, pH or chemical
compounds In the chemical compound, can remove and
have the protein renature or refold
Refolding
STRUKTUR SEKUNDER
Dibentuk dan dipertahankan oleh ikatan hidrogen antara C=O dengan NH pada ikatan peptida
Helix ά (3,6 asam amino), prolin (penyelang kesinambungan)
Lembaran β (R berganti-ganti diatas/dibawah tulang punggung).
Protein Folding
2 regular folding patterns have been identified – formed between the bonds of the peptide backbone
-helix – protein turns like a spiral – fibrous proteins (hair, nails, horns)
-sheet – protein folds back on itself as in a ribbon –globular protein
Beta-pleated sheet
The structural properties of silk are due to beta pleated sheets.The presence of so many hydrogen bonds makes each silk fiber stronger than steel.
Sheets Core of many proteins is the
sheet Form rigid structures with the H-
bond Can be of 2 types
Anti-parallel – run in an opposite direction of its neighbor (A)
Parallel – run in the same direction with longer looping sections between them (B)
Alpha-helix
Helix
Formed by a H-bond between every 4th peptide bond – C=O to N-H
Usually in proteins that span a membrane
The helix can either coil to the right or the left
Can also coil around each other – coiled-coil shape – a framework for structural proteins such as nails and skin
Struktur Tersier Protein
Interaksi ion, hidrofobik, ikatan disulfida, ikatan kovalen
Protein fibrosa (serat-serat panjang, tongkat atau tali: kolagen, keratin)
Protein globuler (bulat, mudah larut dalam air/garam encer): Myoglobin, ribonuclease
KOLAGEN
Protein terbanyak dalam tubuh manusia high Glycine, Proline, & no Cysteine when
boiled makes gelatin 3 heliks kolagen: tropokolagen
Kolagen (lanjutan)
Keratin
Keratin ά : kulit, rambut, kuku high basic aa's (Arg, His, Lys), but with Cys Membentuk serat, tongkat yang panjang dapat diregang bila basah
Keratin ά
Keratin (lanjutan)
Silk Keratin β: sutera, paruh burung Bentuk lembaran bergelombang tidak dapat diregang bila basah
Struktur Kuarterner
Penataan suatu rantai protein dengan protein lain dan dengan koenzim, tidak terikat secara kovalen
Hemoglobin, mioglobin, protein plasma, immunoglobulin, protein yang diperlukan untuk membawa Fe dan Cu
Hemoglobin & Immunoglobulin
PROTEIN KOMPLEK
lipoproteins –(+ lipids)blood, membrane, and transport proteins
glycoproteins - (+ carbohydrates)antibodies, cell surface proteins
nucleoproteins - (+
nucleic acids) ribosomes & organelles
Denaturasi dan Renaturasi Protein
DENATURATION loss of 3-D conformation by heat, pH, organic solvents, detergents
RENATURATION - regaining of biological activity via self-assembly
Denature and Renature
Sickle cell anemia
Determinasi Struktur Protein
Molecular exclusion/gel filtration chromatography
Amino Acid Sequencing
Mass Spectrometry : detects exact MASS of small peptides.
X-Ray Crystallography : determines 3-D shape of molecules mathematically.
NMR Spectroscopy : magnetic signal indicate distances between atoms.
The three-dimensional shapes of over 10,000 proteins have been determined using X-ray crystallograghy and NMR.
PEMISAHAN DAN DETEKSI PROTEIN
PEMISAHAN DAN DETEKSI PROTEIN
Determinasi Struktur Protein